Attempts have been made to reduce or mask noise generated during a brake application such as through: the application of a sound coating on backing plates as disclosed in U.S. Pat. No. 3,998,301; the location of a screen member between the friction member and backing plate as disclosed in U.S. Pat. No. 4,154,322; the use of discrete friction members as disclosed in U.S. Pat. No. 4,315,563 and U.K. Patent 2148424A; the selection of the shape of a friction pad such that its engagement surface is less than the nodal diameter of a frequency that would create undesirable noise as disclosed in U.S. Pat. Nos. 4,705,146 and 5,145,037; and the modification of ingredients in the friction material. Such methods and/or structure to reduce noise have not been widely accepted by the automobile industry primarily because of the added cost associate for such brake systems.
It is known that most structures vibrate and such vibration is often the result of dynamic forces applied to such structures which can create noise. If the vibration of the structures is in a frequency domain which is not audible, most individuals are not conscience aware of the occurrence of such vibration, However, such vibration can be measured and an analysis of such vibration can be evaluated as a product of the structure response spectrum and the spectrum of an applied dynamic force through frequency response analysis. Most often the structure response is studied through modal analysis wherein modal parameters of the structure (natural frequencies, modal damping and mode shapes) are identified and ultimately a modal model of the structure is constructed based on these modal parameters. From experimentation, it has been determined that noise is generated in all brake systems during each brake application, however only audible noise is objectionable to most drivers.